A thermoplastic elastomer (i.e., TPE) is a polymeric material exhibiting a thermoplasticity similar to a thermoplastic resin at a high temperature and exhibiting a rubber elasticity similar to an elastomer at an ordinary temperature. Generally, by a blend of a thermoplastic resin and elastomer containing the domain phase of an elastomer closely and uniformly dispersed in a continuous phase of a thermoplastic resin, the characteristic properties of TPE are exhibited. On the other hand, a polymer blend prepared by a dynamically cross-linking process of mixing a cross-linkable elastomer in a continuous phase of a thermoplastic resin, cross-linking the elastomer in a kneaded state, and finely dispersing the cross-linkable elastomer in the continuous phase exhibits the characteristic properties of TPE and has superior characteristic properties compared with a simple blend of the two polymer components. Rubber. Chem. Technol. 55, 116 (1982) and U.S. Pat. No. 3,037,954 disclose technologies for the preparation of TPE by dynamic cross-linking and describe, among these, using polypropylene as the thermoplastic resin and butyl rubber as the cross-linkable elastomer to prepare a PP/IIR-based TPE, wherein, the cross-linking of the butyl rubber uses resin cross-linking.
Butyl rubber has an extremely low degree of unsaturation, and therefore, is excellent in weatherability, heat resistance, ozone resistance, etc. and is also has a low air permeability, and, therefore, is suitable for use as a sealant, adhesive, etc. As methods for cross-linking the butyl rubber, sulfur cross-linking, quinoid cross-linking, resin cross-linking, etc. are known, but currently it is hard to say that any method is satisfactory in practice. That is, sulfur cross-linking requires cross-linking at a high temperature over a long time. Further, quinoid cross-linking usually uses toxic red lead oxide as an oxidizing agent to activate the quinoid and, therefore has environmental problems. Further, resin cross-linking has a remarkably slow reaction rate and requires heating at a high temperature over a long time. Thus, the result is liable to be a product in a state not completely cross-linked, and therefore there is the problem that, during the use thereof, a cross-linking reaction is liable to occur and the physical properties are liable to greatly change. Further, among the methods of cross-linking a diene-based rubber, etc., the cross-linking with an organic peroxide, which is extremely excellent in heat resistance, is almost never used as a method for cross-linking butyl rubber. This is because, if this cross-linking is applied to butyl rubber, the decomposition reaction of the main chain is liable to occur in preference to the cross-linking and the resultant product is liable to be softened rather than cross-linked. On the other hand, partially cross-linked butyl rubber is commercially available as a butyl rubber capable of being cross-linked with an organic peroxide, but this has the problem of insufficient processability. Further, Japanese Patent Publication (A) No. 6-172547 discloses a method of cross-linking an un-crosslinked butyl rubber in the presence of an organic peroxide and a polyfunctional monomer containing an electron-attractive group, but, according to this method, severe reversion is liable to occur.
The present inventors previously found a modified butyl rubber composition including a modified butyl rubber capable of being cross-linked with an organic peroxide by adding, to the butyl rubber, (a) a compound such as TEMPO (i.e., 2,2,6,6-tetramethylpiperidine 1-oxyl) derivative stable at an ordinary temperature even in the presence of oxygen and having, in the molecule thereof, a nitroxide-free radical, (b) a radical initiator and (c) a bifunctional or higher functional radical polymerizable monomer, followed by reacting the mixture (see Japanese Patent Application No. 2006-131780). Thus, as stated above, the TPE of butyl rubber/polyolefin is currently dynamically cross-linked by resin cross-linking. There are no examples in which dynamic cross-linking by peroxide cross-linking is applied to the butyl rubber/polyolefin.